Optoelectronic devices have been used to generate and detect picosecond and subpicosecond pulses. One popular type of device includes coplanar strip transmission lines deposited over photoconductive material such as ion-implanted (radiation damaged) silicon-on-sapphire. In such a device, the pulses are generated when a charged transmission line is temporarily shorted by carriers excited within the photoconductive material. Minimum electrical pulse width is determined by the lifetime of photoexcited carriers in the photoconductive material. Examples of photoconductive detectors are shown in articles by D. H. Auston et al., Appl. Phys. Lett., 36 (1), pp. 66-8 (1980); D. H. Auston et al., Appl. Phys. Lett., 37 (4), pp. 371-2 (1980); P. R. Smith et al., Appl. Phys. Lett., 38 (1), pp. 47-50 (1981); W. G. Gallagher et al., Appl. Phys. Lett., 50 (6), pp. 350-2 (1987); and M. B. Ketchen et al., Appl. Phys. Lett., 48 (12), pp. 751-3 (1986).
For coplanar transmission lines on a photoconductive substrate, response or "rise time" of the photoconductive detector is in the picosecond regime while quantum efficiencies for such a detector are quite low. In the prior art, it is only the streak camera which has offered both fast response times and high sensitivity. However, usefulness of the streak camera is offset by its high cost in relation to the formerly described transmission line devices.